Pulse shaping circuit



y 10, 1951 w. E. GLENN, JR 2,560,167

PULSE SHAPING CIRCUIT Filed Nov. 22, 1949 a iii Arrows/5x Patented July 10, 1951 "William- E: Glenn, Jr.,

Berkeley; Calif., assignor r to the United -States of. America, as represented "bythe United States Atomic. Energy, Commisa sion 4 Application November 22; 1949, Serial N 128,7 '72 Claims.

This:invention-relates;.to a: circuit network v and more particularly to a pulsesha'ping circuit. Many 'forms iof fpulseifsha'ping circuits have beendeveloped lforvarious: types. of electronic 1 devices' to developpulses"of'voltage havinga icertain predetermined height and duration with re-.. "spect to a reference orinput pulse of voltage. In I 1 many "instances: it has been" found. desirable to reduce the width and to square or flatten the top of a given pulse of voltageri Heretofore, complex circuits requiring 'amany tubes and associated circuitelements: haveb'een' devised to accomplish such pulse height squaringt: and: .width :reduction in an accuratesand .lpredetermined -imanner. It

12 hasheen found that. excellent. results areattained by. arelatively simple :circuit comprising a com.- binationi' 'of apulsesharpener; an amplifier,v a pulse. flattening. network, and an'. output circuit.

The output voltage of: this circuitithenaccurately bears a" predeterminedrelationship .Withthe i height" of. the input :pulse. of :voltage: :and :has a predetermined :duration.

-: It. is therefore an Iobject .of the-presentinvention .to. provide a: new: andi".improved. :.pulse .shaping circuit.

Another :object ofithe' present invention is :to

-- provide a pulse shapingcircuiticomprisinga.pulse 2 sharpener; ran amplifier, a=tpulse flatteningcir- ...cuit,.and a cathodei'follower outputcircuit.

.- A .further 'objectiof :the apresentLinvention: is

' to provide a pulse: shaping. circuit 1 for. developing .the duration of an output .pulse.

Another imp'ort'ant. object ofthe present linvention is toiaprovide a network comprising a condensertand apair 1of2diode crystals fOI'JSQllZtring or flattening the developed pulseofflvolta'ge siwithout sacrificing pulse height proportionality.

.Still another object :ofthe invention is to .pro- .vide apulse shaping. circuitof simpleiconstruction utilizing: commercial radio .parts'well within their rating.

vvOther objects and advantages will be apparent in the following description considered together 4 with the accompanying drawing, iniwhich:

:Figure l is a schematic wiring diagramem- :r. .bo'dying.-.the invention.;? and Fig- 2- is a series of timecorrelated voltage l --wave forms representing voltages at @various points in the circuit.

2 Referring now to the drawing in detail, and Fig. 1 in particular, there is shown a triodetube Ll I: which'is connected'in 'the form of a pulse sharpener. The control. grid of the tube H is :1directly1connected to an input terminal 12. A resistor I 3 isconnected'fromthe control grid of thetube I I to ground to develop a bias voltage for thetubefromthe input voltage. To provide an 1: operating voltage rforythe tube H the anode. s connected to a suitable conventional source #4 of :unidirectional voltage *through a dropping .zresistor 16. To provide degeneration in the circuit of the tube .l l, a potentiometer H and a resistor 18 are series'connectedbetween the cathode and ground. ;3AS a means of. developing a pulse having a;predeterminedrduration a section of an open circuit artificial transmission line l9'is'connected to thejunction between the potentiometer 'l'l andthe resistor l8. 'The'transmission line i9 20 is: preferably comprised of a plurality of suitably -connected inductors. and condensers, the values of which are chosen to give a desiredtime constant to the'lineand to pass a broad band of frequencies. Theoperation of the circuit willbe more iully'described hereinafter.

- The voltage at :the' anodeof .the tube I" is coupledto-the control grid of apentode-tube 2! through a coupling condenser 22 and is developed 1 across a grid bias resistor 23 which is connected between the control grid and ground. The connections of the. tube 2| .are inthe form of a 1 conventional :wide bandpass amplifier and are as r followsr-the anode is connected to the voltage source l i'through a dropping resistor '24, the suppressor grid is directly connected to the ':cathode,. the screen grid is connected to the voltage source l ithrough a droppingresistor '26 and to groundthrough a by-pass condenser '21, and thecathode is connected to ground'through 4 acathode resistor 28. The principal purpose 'of this amplifier tube 2| is to invert the output 'of the tube II and afiord 'distortionless amplification.

The voltage appearing: at'-the anode of the tube 2| ,is'connected to the control grid of a triodetube 3| through a condenser 32 and is de- 'veloped across a grid bias resistor 33. The tube 3l-is connected in the form of a cathode follower 'with'the anode directly connected to thevoltage source 14 and the cathode connected to ground through tWOFSGIlGSfCOIlIlGCtBd. resistors 34 :and36.

To flattenor square the top of the pulse of voltage appearing .across the resistor.36,'the common pointibetween the resistors 3 and 36 is connected fifistotone sideof. a:condenserz3l through a crystal '....diode 38.;,which disconnected improper. .polarity so that current will pass when the common point between the resistors is more positive. The other side of the condenser 37 is connected to ground to complete the connection. As a means of discharging the condenser 31, a second crystal diode 39 is connected between the ungrounded side of the condenser to the cathode of the tube 3| in such polarity that current will pass when the condenser is charged more positivel than the cathode of the tube 3 The voltage across the condenser 37 is connected to the control grid of a triode tube 4| connected as a cathode follower which serves as the output circuit. The anode of the tube 4| is directly connected to the voltage source l4 and the cathode is connected to ground through a cathode resistor 12. The voltage across the cathode resistor 42 is utilized as the output voltage of the pulse shaping circuit and, therefore, the cathode of the tube 4| is connected to an output terminal 43.

Now consider the operation of the present invention constructed in accordance with the foregoing description and suitably supplied with an operating voltage from the conventional voltage source is. The heater elements of the tubes 2|, 3|, and 4| are properly energized by a suitable source of voltage (not shown). Under these conditions a positive pulse of voltage, having a;

waveform 5| as shown'on Fig. 2, impressed at the input terminal l2 raises the potential of the control grid of the tube 2 I, thereby making the tube conductive. For proper operation of the circuit the potentiometer I7 is adjusted so that the im pedance from the junction between the potentiometer I1 and the resistor l8 to ground is substantially equal to the characteristic impedance of the chosen artificial transmission line |9. The above-mentioned characteristic impedance easily calculated by using well known artificial transmission line formulae and substituting the values of the lumped constants of the line therein. The value of the resistance to which the potentiometer I! is adjusted to make the input impedance to the transmission line l9 approximately equivalent to the characteristic impedance of the line I9 is easily calculated by the use of the formula for the output impedance of a cathode follower having equivalent circuit elements.

As the tube conducts and current flows in the cathode circuit, a voltage wave approximately equal to one-half of the applied grid voltage equal to one-half of the value of input pulse of voltage. At a time twice the time constant of the selected artificial line, the line is fully charged to approximately the value of the input pulse of voltage. Since the input impedance of the line I!) has been adjusted by the potentiometer I! to be substantially equal to the characteristic impedance of the line, there will be no further reflected waves and the waveform 52, as shown on Fig. 2, is representative of the voltage at the input to the line.

Now, since the current flowing through the resistor I8 is the same as that through the dropping resistor IB, the voltage developed across the resistor l6 becomes a square wave 53 having a stepped appearance, as shown on Fig. 2, which is the difference between the grid and cathode voltages of the tube II, as shown by the waveforms 5| and 52, respectively, on Fig. 2. The

voltage then, as taken from the anode of the tube II and coupled to the control grid of'the tube 2|, is proportional in height to the input pulse of voltage and has a duration approximately equivalent to twice the time constant. of the artificial transmission line |9.

As stated previously, the tube 2| and associated circuit elements are interconnected in the form. of a conventional amplifier. Therefore the pulse of voltage developed at the anode of the tube 2| is amplified and inverted by the tube 2| so that the voltage has a waveform 54, as shown on Fig. 2.

- lower tube 3| having a flattening network contravels the length of the line |9. The latter occurs because the maximum resistance of the potentiometer I1 is chosen to be low ascompared to the resistance of the resistor l8 and 'because the cathode voltage of a tube connected in the manner of tube follows the grid voltage and has approximately the value thereof. It is well known that a pulse of voltage applied to an open circuit transmission line will start a traveling wave from the input end which charges the line to one-half the value'of the applied voltage during the time it takes such a traveling waveto traverse the length of line. Since the output end of the line is open, a reflected Wave of onehalf the value of the applied voltage is formed which then charges the line to the full value of the applied voltage during the time of travel back to the input end of the line. Therefore current flow through the tube causes a voltage todevelop across the input to the transmission line, which is approximately equal to the value of the input voltage of thetube II and starts a traveling Wave down the line |9which is approximately nected into the cathode circuit. Since the oathode follows the control grid voltage, a positive pulse of voltage having the waveform 54 is divided across the two cathode resistors 34 and 36. The voltage across the resistor 36 then has the waveform 55, as shown on Fig. 2, which is similar to waveform 54, but reduced in height by a constant fractional amount. It will be readily apparent that, at the time the voltage at the junction between the two resistors 34 and 36 becomes more positive than the condenser 31, a charging current will flow through the diode crystal 38 to charge the condenser 31. Since the maximum value of voltage of the pulse occurs at the leading edge thereof, the condenser will be charged to a maximum value immediately. With the diode crystal 39 connected between the condenser 31 and the cathode'of the tube 3| in such polarity that the condenser can discharge therethrough only when the cathode is less positive than the condenser, the condenser will maintain the maximum charge until such time as the trailing edge of the pulse occurs. Thus the voltage across the condenser 31 is substantially a rectangular wave 56, as shown on Fig. 2, and has a flattened top.

Provided as a low impedance output for the pulse shaping circuit is a triode cathode follower tube 4|. The voltage across the condenser 31 is coupled to the control grid of the cathode follower tube 4| and the output voltage having a waveform 56, as shown on Fig. 2, is supplied to the output terminal 43.

From the foregoing it is seen that from an input pulse of voltage having a trailing, trailing-edge, a pulse of voltage has been formed with a flat top, a definite predetermined duration, and a height proportional to the height of the input of voltage.

While the salient features of the invention have been described in detail with respect to a particular embodiment it will, of course, be apparent that numerous modifications may be made within the spirit and scope of this invention, and it is therefore not desired to limit the invention to the exact details shown except insofar as they may be defined in the following claims.

"What is claimed is:

1. A pulse shaping circuit comprising an electron tube having at least an anode, a control grid, and a cathode, source means connected to said anode for applying an operating voltage thereto, means for impressing a signal pulse of voltage on said control grid, a circuit network connected to said cathode and including a pair of series resistors with one end of an open circuit artificial transmission line connected to the junction between said resistors, amplifying means for inverting the pulse of voltage developed at said anode, and cathode follower means connected to said amplifying means and having a diode gating circuit connected in the cathode circuit of said cathode follower for flattening the top of said inverted pulse of voltage.

2. A pulse shaping circuit comprising an electron tube having at least an anode, a control grid, and a cathode, source means connected to said anode for supplying an operating voltage thereto, means for impressing a signal pulse of voltage on said control grid, a potentiometer and a resistor series connected between said cathode and ground respectively, an open circuit artificial transmission line connected to the junction between said potentiometer and said resistor, said potentiometer being adjusted so that the input impedance to said line is substantially equal to the characteristic impedance of said line, amplifying means for inverting the resultant pulse of voltage developed at said anode which is the difierence between the voltage at said control grid and cathode, and cathode follower means connected to said amplifying means and having a diode gating circuit connected in the cathode circuit of said cathode follower for flattening the top of said inverted pulse of voltage.

3. A pulse shapin circuit comprising an open circuit delay line pulse sharpener, an amplifier connected to the output of said pulse sharpener, and a cathode follower connected to said amplifier, said cathode follower having a pair of series connected resistors connected between the oathode and ground, a first diode crystal connected at one end to the junction between said resistors and at the other end to one side of a condenser the other side of which is connected to ground, a second diode crystal being connected between the ungrounded side of said condenser and said cathode, the polarity of said diode crystals being such that a current will flow through said first crystal when the junction between said resistors is more positive than said condenser and through said second crystal when the condenser is more positive than said cathode.

4. A pulse shapin circuit comprising an open circuit delay line pulse sharpener, an amplifier connected to the output of said pulse sharpener, and a cathode follower connected to said amplifier, a first resistor having one end thereof connected to the cathode of said cathode follower, a second resistor connected between the other end of said first resistor and ground, a first and second rectifying means connected in series across said first resistor, and condenser means connected between the junction of said rectifying means and ground, the polarity of said rectifying means being such that current will flow through the first when said condenser is less positive than the resistor common point and through the second when said condenser is more positive than said cathode.

5. A pulse shaping circuit comprising a triode tube having an open circuit transmission line connected across a resistor in the cathode circuit thereof, the control grid of said tube being connected to a source of positive pulses, means connected to the anode of said tube for supplying an operating voltage thereto, amplifying means connected to the anode of said tube to invert voltage variations thereat, a cathode follower circuit connected to said amplifying means, a pair of diode rectifiers series connected across a portion of a voltage divider in the oathode circuit of said cathode follower so that conduction will occur toward the cathode of said cathode follower, a storage condenser connected to the junction between said rectifiers, and a cathode follower output circuit connected across said condenser.

WILLIAM E. GLENN, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,255,839 Wilson Sept. 16, 1941 2,266,154 Blumlein Dec, 16, 1941 

